Mail server 4.5
Google mail client on Android does not accept the certificate. So it is not Let's Encrypt. Although updated today.
I understand that the problem is in the postfix config.
How to specify the correct path to Let's Encrypt?
In the config smtpd_tls_chain_files = /etc/ssl/private/ssl-cert-snakeoil.key,/etc/ssl/certs/ssl-cert-snakeoil.pem
should I also specify the paths to the certificates for Dovecot?

smtpd_tls_cert_file = /www/server/panel/vhost/cert/yourdomain/fullchain.pem
smtpd_tls_key_file = /www/server/panel/vhost/cert/yourdomain/private.key
smtpd_tls_CAfile = /www/server/panel/vhost/cert/yourdomain/chain.pem
is that correct?

    At the same time, check the postfix configuration, which can be viewed in the server status
    "mail.135mailtest.com" is replaced with your domain name
    Put:
    smtpd_tls_chain_files=/etc/ssl/private/ssl-cert-snakeoil.key,/etc/ssl/certs/ssl-cert-snakeoil.pem
    Change to:
    smtpd_tls_chain_files = /www/server/panel/plugin/mail_sys/cert/135mailtest.com/privkey.pem,/www/server/panel/plugin/mail_sys/cert/135mailtest.com/fullchain.pem
    Note to replace 135mailtest.com with your domain name.
    Also check /www/server/panel/plugin/mail_sys/cert/135mailtest.com/ for privkey.pem and fullchain.pem files

    You can use this command to check whether the correct SSL is configured
    openssl s_client -connect mail.135mailtest.com:587 -starttls smtp
    or
    openssl s_client -connect mail.135mailtest.com:465

    If the display is not OK, try to save the SSL certificate again, or please re-apply for SSL

    aaP_randreevich

        aaPanel_Kern

        smtpd_tls_chain_files = /www/server/panel/plugin/mail_sys/cert/135mailtest.com/privkey.pem,/www/server/panel/plugin/mail_sys/cert/135mailtest.com/fullchain.pem

        The subdomain mail.135mailtest.com was specified
        And there was an error: Verify return code: 21 (unable to verify the first certificate)
        There is no error now, but Outlook says

        that the server does not support the specified connection encryption type.

            aaPanel_Kern
            smtpd_tls_chain_files = /www/server/panel/plugin/mail_sys/cert/example.com/privkey.pem,/www/server/panel/plugin/mail_sys/cert/mail.example.com/fullchain.pem

            indicate on the way example.com or mail.example.com ?

            After changing the path, should I recreate the certificate?

              I restored VPS from backup, updated the certificate again. I didn't change the line
              smtpd_tls_chain_files = /etc/ssl/private/ssl-cert-snakeoil.key,/etc/ssl/certs/ssl-cert-snakeoil.pem
              Google client doesn't give any errors.
              openssl s_client -connect mail.example.com:587 -starttls smtp
              checks pass without errors.
              It's not clear.